1. Field of the Invention
The present invention generally relates to a light emitting diode chip (LED chip) and a manufacturing method thereof, and more particularly, to an LED chip with good reliability and a manufacturing method thereof.
2. Description of Related Art
Due to advantages of long lifetime, small volume, high shock absorption, low heat and power saving, LEDs have been widely used in household appliances and indicators or light sources of various instruments. In recent years, LEDs are developing towards rich colorfulness and high luminance, so that the applications of LEDs have been expanded to mega-size display board, traffic light, and so on. It can be expected LEDs can substitute tungsten lamps and mercury lamps in future and become lighting sources with electricity-saving and environmental friendly functions.
In the prior art, LEDs can be fabricated through forming a gallium nitride (GaN) epitaxy layer on a sapphire substrate. The method is suitable to fabricate GaN LEDs on sapphire substrates by using semiconductor process. The disadvantage of the above-mentioned method is that the fabricated GaN LEDs are located on a sapphire substrate, which limits the insulation and heat-dissipating efficiency of the GaN LEDs.
To solve the above-mentioned problem, U.S. Pat. No. 7,250,638 provides a vertical type GaN LED. To fabricate the vertical type GaN LED, a wafer level bonding process and a laser lift-off process are used to separate the formed GaN epitaxy layer from the sapphire substrate. Then, the GaN epitaxy layer is placed on a permanent substrate with good electric conductivity and thermal conductivity. Ultimately, electrodes are fabricated so as to form an LED chip. In U.S. Pat. No. 7,250,638, the GaN epitaxy layer is patterned to form a plurality of LEDs separated from each other, and then a protection layer is formed on the side wall of the patterned GaN epitaxy layer. Afterward, the above-mentioned wafer level bonding process and laser lift-off process are performed.
FIG. 1A is a cross-sectional view of a conventional LED chip during a wafer bonding process and FIG. 1B is a cross-sectional view of a conventional LED chip during a laser lift-off process. Referring to FIG. 1A, an LED chip 100 formed on a growth substrate S1 includes a GaN epitaxy layer 110, a bonding layer 120 and a protection layer 130, wherein the bonding layer 120 is disposed on the GaN epitaxy layer 110, and the protection layer 130 covers a part of the bonding layer 120 and the side walls of the GaN epitaxy layer 110. In more details, the protection layer 130 extends along the side walls of the GaN epitaxy layer 110 and reaches the growth substrate S1. In addition, the GaN epitaxy layer 110 is bonded with a supporting substrate S2 through the bonding layer 120, so that the LED chip 100 is located between the growth substrate S1 and the supporting substrate S2.
Referring to FIG. 1B, a laser lift-off process is performed, wherein laser L irradiates the interface between the GaN epitaxy layer 110 and the growth substrate S1 during the laser lift-off process. At this time, the GaN material at the boundary between the GaN epitaxy layer 110 and the growth substrate S1 is vaporized into gas-phase gallium (Ga) and nitrogen gas (N2) such that the GaN epitaxy layer 110 is separated from the growth substrate S1. However, when the laser L irradiates the interface between the GaN epitaxy layer 110 and the growth substrate S1, a quite large barometric pressure is produced by the above-mentioned gases between the GaN epitaxy layer 110 and the growth substrate S1. The gases with high pressure cause peeling of the protection layer 130 formed on the side walls of the GaN epitaxy layer 110, which results in poor reliability.